Near-death experiences (NDEs) are a widely reported yet poorly understood phenomenon. Though there is no agreed-upon definition of an NDE, it has been described as "profound psychological events with transcendental and mystical elements, typically occurring in individuals close to death or in situations of intense physical or emotional danger," according to a study published in the Yearbook of Intensive Care and Emergency Medicine 2009. NDEs are reported in 4 to 9 percent of the population and among nearly 23 percent of patients who are critically ill. Healthy individuals who think they are in danger may also experience them.

With the improvement  of technology and resuscitation techniques, people have become more curious about this topic. The 2012 book Proof of Heaven, written by retired American neurosurgeon Eben Alexander, popularized the concept of NDEs. As he lay close to death, in a coma caused by a brain infection, he had a transformative experience that included traveling through a black void "brimming over with light: a light that seemed to come from a brilliant orb," he said, accordingt o BBC Science Focus magazine.

Such experiences, for which we have only the subjective reports of patients, usually occur when an individual is in "transitory and reversible cardiac arrest," which is another way of saying, "clinically dead." Without resuscitation and other interventions, recovery of brain function more than three minutes after a cardiac arrest is rare. For a person to be dead, however, the U.S. Uniform Determination of Death Act requires that physicians decide, by applying prevailing clinical criteria, that cardiorespiratory or brain functions are absent and cannot be restored.

Patients who have had NDEs often report having heard themselves being pronounced dead. Still, far from experiencing alarm, they report feeling a sense of peace. These accounts frequently include hearing unusual noises, seeing a dark tunnel, experiencing out-of-body sensations, encountering spiritual beings, witnessing a bright light or a "being of light," entering a realm of bewildering spirits, sensing a boundary or limit, and finally, returning to their physical bodies. According to the study published in 2009, interviews with individuals who have had NDEs have pointed out five stages that occur in the following order: "(1) a feeling of peace and well-being; (2) separation from the physical body; (3) entering a region of darkness; (4) seeing a bright light; and (5) going through the light and entering another realm."

Origin of the Term

The term "near-death experience" was coined by physician Raymond Moody in 1975, who used it in the context of out-of-body experiences, although the term had been used three years earlier by John C. Lilly. In his book Life After Life (1976), Moody claimed that 150 near-death survivors reported positive visionary experiences of passing down a dark tunnel toward a bright light. But descriptions of these experiences go back further.

The French term expérience de mort imminente (experience of imminent death) was proposed by French psychologist and epistemologist Victor Egger in the 1890s. Such experiences were noted by clinicians based on observations of workers who had fallen from scaffolds, soldiers who had suffered terrible injuries on the battlefield, and climbers who had tumbled from slopes. In 1968, Celia Green published an analysis of 400 first-hand accounts of out-of-body experiences. She was the first to see NDEs as experiences worth investigating rather than as anomalous perceptions or hallucinations.

Who Reports a Near-Death Experience?

Scientists have tried to explain how and why NDEs occur. There are two scales typically used to measure NDEs based on subjective accounts: The Weighted Core Experience Index (WCEI) and the NDE scale created by Greyson. The WCEI has 10 components, which are scored based on their presence or absence. (The maximum score is 29.)

Clinical studies suggest that the characteristics of NDEs do not vary by culture. However, some researchers have revealed differences. "The variability across cultures is most likely to be due to our interpretation and verbalizing of such esoteric events through the filters of language, cultural experiences, religion, education and their influence on our belief systems either shedding influence as an individual variable or more often perhaps by their rich interplay between these factors," stated a 2008 study published in the journal Transcultural Psychiatry.

The frequency of these experiences in survivors of cardiac arrest varies from 2 to 13 percent, and they seem to be more common in younger patients. Significantly more patients who had an NDE, especially a deep experience, died within 30 days of being resuscitated, a 2001 Lancet study found, adding that "[t]he process of transformation after NDE took several years, and differed from those of patients who survived cardiac arrest without NDE."

The Lancet study also stated that 62 (18 percent) of 344 cardiac arrest survivors reported a near-death experience, and 41 of them scored six or more on the WCEI. Also, there were no reports of patients experiencing distressing NDEs. Factors such as medication, fear of death before cardiac arrest, and the duration of the NDE were ruled out as possible explanations for why the patients had the experience. However, people below age 60 were more likely than older people to report an NDE, along with people suffering their first myocardial infarction. Women were more likely to report vivid NDEs after surviving cardiac arrest, and they tended to be older: 66 versus 61 years of age for male survivors.

In another study published by Signa Vitae in 2011, researchers showed that the severity of a life-threatening situation was associated with a higher incidence of NDEs, suggesting that they are more likely to occur in patients who find themselves "closer to death or have a lesser possibility for survival."

The Organic Explanation

Researchers Dr. Charlotte Martial, Coma Science Group at the University Hospital of Liège, and Chris Timmermann, Imperial College Psychedelic Research Group, believe that there is a "scientific, neurochemical explanation for NDEs," according to the 2020 article in BBC Science Focus. Martial said she is "very convinced by such explanations." However, Timmerman acknowledges that "definite proof might be impossible with our current tools because it would require researchers to probe the brains of human beings at the moment of death, which is unethical."

Many scientists, however, believe that even without the limitations Timmerman cites, they can still conclude that NDEs are the result of chemically induced brain functions when the brain is under stress. To explain the phenomenon, researchers have theorized that it results from endorphin-induced limbic brain activity, altered temporal lobe activity, and anoxic seizures due to a sudden lack of oxygen in the brain. They have also proposed ketamine-like endogenous hallucinogens, cerebral hypoxia (a lack of oxygen) or hypercarbia (an excess of CO2), an excess of serotonin or endorphins, and responses to prescribed drugs as causative factors.

Significant epileptiform electroencephalographic (EEG) activity, as seen in epilepsy, has also been observed in individuals who reported having an NDE when compared with control patients.

During cardiac arrest, brain activity is assumed to be diminishing. Nonetheless, researchers who conducted studies on rats have found more brain activity than they initially expected, thanks to brain scans that reveal a surge of synchronized gamma oscillations as well as high levels of interregional coherence and feedback connectivity, all of which may account for NDEs. Another theory, shared in the 2017 book Coma and Disorders of Consciousness, edited by Caroline Schnakers and Steven Laureys, suggests that impaired cerebral oxygen levels in the context of a cardiac arrest might lead to a disruption of the physiological balance between conscious and unconscious states, resulting in rapid eye movement (REM) sleep, which could cause visual hallucinations. Some of those who have reported experiencing an NDE have also been found to be more sensitive to being woken during REM sleep and sleep paralysis.

"Of course, the brain does funny things when it's running out of oxygen," wrote the neuroscientist Colin Blakemore. He added, "The odd perceptions are just the consequences of confused activity in the temporal lobes."

Psychological Explanation

Psychological models proposed to explain NDEs have focused on dissociative, protective mechanisms that might manifest as wish-fulfilling hallucinations in a situation of danger. These mechanisms might also lead to partial or distorted memories when a patient is unconscious. Nonetheless, researchers still have to determine why some people reported an NDE and others, who were also close to death, did not. One explanation is that patients who reported an NDE might be predisposed due to activity in the temporal lobe of the brain. Those who survived an NDE subsequently reported a change in their beliefs, attitudes, or values. They also described having a reduced fear of death, greater motivation, and a better stress response.

Researchers have been unable to determine whether surviving an NDE causes these changes or whether the realization of the closeness to death is responsible for them. Most, however, agreed that surviving an NDE had a profound effect on their family, social, and spiritual relationships, as the effect was not limited to patients alone. A 2012 study of 476 hospital nurses in Italy found that 34 percent of those who had personally encountered NDE were more positive about the phenomenon and the assistance they could provide to their patients than the nursing staff who had not treated such patients.

Is it possible that dying or the awareness of impending death can be a triggering factor for an NDE? As the researcher J.E. Owens and his colleagues have written: "[I]t would seem that among individuals who were not near-death, their experiences could be precipitated by the belief that they were." This is known as the "expectation hypothesis," which postulates that NDEs originate from an altered state of consciousness triggered by a life-threatening condition that, without medical care, could result in death.

In cases like this, the individual's system of beliefs and expectations of both dying and a possible afterlife might make the occurrence of an NDE more likely. Another theory, known as the "depersonalization and dissociation hypothesis," postulates that, upon facing a life-threatening situation, an individual disconnects from the external world and experiences fantasies as a projective defense mechanism to make the imminence of death more comprehensible and less distressing, according to Coma and Disorders of Consciousness.

An Integrative Model

An integrative mode lof organic theories has proposed that traumatic events cause brain stress. This model suggests that the release of neurotransmitters produces effects such as analgesia (the inability to feel pain), euphoria, and detachment. These effects, along with decreases in oxygen, can lead to hallucinations and a detached perspective on one's life. As these neurotransmitters travel through the brain, they can produce further hallucinations and the sensation of seeing a bright light.

Many of the key features of an NDE bear remarkable similarities to those seen in people who have taken psychedelic drugs. Psychedelics act on the serotonergic system in the brain (the system in the brain which controls the neurotransmitter serotonin and is involved in mood and perception, along with other functions). Such psychedelics include lysergic acid diethylamide (LSD), psilocybin (the hallucinogenic compound in magic mushrooms), and dimethyltryptamine (DMT), or the "spirit molecule," found in many plants of the Amazon basin.

A team led by Timmermann and Robin Carhart-Harris at Imperial College, including Martial in Belgium, in 2018, observed "few discernible differences" between actual NDEs and experiences induced by DMT. This view is based on the similarity of the "first-person descriptions of approximately 15,000 psychedelic ‘trips' with the retrospective first-person accounts of several hundred NDEs collected in Belgium and the USA," stated Science Focus. According to the interpretation given by these scientists, the NDEs were much like drug-induced trips, especially for those who had taken ketamine, a "dissociative psychedelic" that is used as an anesthetic.

Still, there are disagreements among some experts. International psychedelics expert David E. Nichols argued in a 2018 paper "that the concentrations of DMT in the brain are too minute to be responsible for the psychoactive effects observed during NDEs. However, he says that ‘as a scientist, I do believe there is a neurochemical explanation for an NDE,'" added the Science Focus article. He did admit that since no one has come back from the dead to report what happened to them, no one can be sure that a drug such as DMT or ketamine is a valuable model for an NDE.

A First-Person Account of an NDE

The well-known journalist and writer Sebastian Junger (author of the bestselling bookThe Perfect Storm) recounts his own NDE experience in his 2025 bookIn My Time of Dying: How I Came Face-to-Face with the Idea of an Afterlife. In an interview with Maria Schriver's Sunday Paper, he discussed how common NDEs are: "They happen in societies around the world and certainly have happened forever. Our medical knowledge allows doctors to bring people who are dying, like I was, back into the world of the living. We have many more stories of people who are on the threshold and what they remember. There are some medical explanations, but I found them to be not entirely sufficient. Some researchers believe that it's not proof but evidence of some kind of post-death existence. Then other people who are equally well-informed say nonsense, this is neurochemicals, and it's blood oxygen, and it's a form of seizure. So, there are all kinds of straightforward medical explanations for the dying brain having visions."

As he lay dying, he saw his father. "That could have been entirely cooked up by my own dying brain, and it is still comforting. The relationship that we have with the dead continues in our minds until we die. At the very least, the relationship I had in my mind with my father changed. He was very sweet, but he was on the spectrum, and he was hard to reach emotionally as a father. So, I didn't sort of count on him throughout my life and as a child for that baseline emotional support. But then, there he was, and it really did sort of change things for me."

His brush with death made him, an atheist, reconsider his beliefs: "but this all did make me think that possibly on a subatomic or quantum level, we don't really understand existence, life, death, reality, consciousness, or universe and that there's some sort of post-death reality to the individual that we can't —and maybe never will be able to—make sense of and then that's what people keep bumping into around experiences like this."

A Problem for Research

Some scientists, such as Dr. Bruce Greyson, professor emeritus of psychiatry and neurobehavioral sciences at the University of Virginia and co-author of The Handbook of Near-Death Experiences, think that "NDEs …present us with data that are difficult to explain by current physiological or psychological models," he wrote in 2013.

Is it even possible to explain NDEs? Most published works on NDEs are considered both "retrospective and sporadic." These events pose a particular challenge, as there is no certainty about their occurrence and they are generally not reported soon after they happen but rather days, months, or even years later, which can lead to distortions in personal accounts.

"[T]here is currently no consensual or satisfying scientific explanation for NDEs. … The claims that NDEs are evidence for life after death may have contributed to the reluctance of designing rigorous empirical protocols to study such a ‘pseudoscience' phenomenon," states Coma and Disorders of Consciousness. The emerging neurosciences evidence suggests that NDEs can be explained by modifications or alterations of brain functions, leading to an altered state of consciousness in critically ill patients.

Because studies of these events have been limited to a few patients, researchers have also found that it is impossible to determine which factors account for these events. The administration of drugs might also trigger the effect during the period of arrest.

Unpleasant Responses

Not all NDEs are pleasant, nor do they imbue patients with the sense that there is life after death. Studies of patients who have undergone frightening experiences may be challenging to conduct because people are reluctant to report them. These "inverse experiences," as they're called, are often perceived as an alien reality and are highly stressful. Other reports have documented "perceptions of emptiness" and even a "‘hellish' encounter with threatening entities, and various accoutrements of the traditional hell, marked by perceptions of impending judgment and torment," added the book.

These distressing NDEs occur under a wide range of circumstances and feature many of the same elements as pleasant NDEs. Researchers who have reviewed clinical studies spanning decades have been unable to explain why these types of NDEs occur or why specific individuals may be susceptible to them. Theideathat "good" people will have pleasant NDEs and bad people distressing ones has been debunked.

Survivors of an inverse NDE find the experience hostile. One man who got thrown from a horse experienced himself floating "at treetop height, watching emergency medical technicians working over… his body. ‘No! No! This isn't right!' He screamed, ‘Put me back!' but they did not hear him. Next, he was shooting through darkness toward a bright light, flashing past shadowy people who seemed to be deceased family members waiting. He was panic-stricken by the bizarre scenario and his inability to affect what was happening," according to a narrative published in the Missouri Medicine journal in 2014.

An NDE of the "void" is an existential encounter often accompanied by a sense of being alone, isolated, or being annihilated.

In the so-called hellish scenarios, survivors report plummeting to the gates of hell or being escorted through a desolate landscape and encountering wandering spirits that seemed to be lost and in pain. Another survivor, an atheist university professor, described being "torn apart by malevolent beings."

Distressing near-death experiences are both fascinating and frustrating as altered states of consciousness. Because of the deeply rooted concept of hell in Western culture and its Christian association with eternal physical torment, they pose serious challenges to individuals who may shape their lives around such a profoundly durable event, as well as to their families, friends, and physicians. In the absence of clear-cut clinical data and universal cultural views, physicians are advised that neutrality of opinion and careful listening are likely the best professional practice for dealing with distressing near-death experiences.

Long-Term Effects

How people report NDEs appears to be influenced in many respects by the culture they were raised in—for instance, whether they believe that they have glimpsed heaven or hell. Christians tend to see Jesus or St. Peter, Hindus see Brahma, and Buddhists may see the "bardo," or transitional states between reincarnations as described in theTibetan Book of the Dead.

Longitudinal studies have demonstrated long-lasting transformational effects of near-death experiences on a person's understanding of life and self, social attitudes, and a shift in social customs and religious beliefs. Those survivors who have undergone distressing NDEs, on the other hand, may suffer from long-term trauma. One of the principal components of near-death experiences is the out-of-body experience, which is associated with the partial impairment of consciousness and disruption of normal bodily functions.

According to the Near-Death Experience Research Foundation, which has collected more than 5,000 accounts from across the world, most survivors reported a sense of peace and energy when they felt as though they were dying. They observed that time did not exist during these experiences. Marieta Pehlivanova, a research assistant professor of psychiatry and neurobehavioral sciences at the University of Virginia School of Medicine's Division of Perceptual Studies, noted during an interview that those who had a brush with death and did not have an NDE also experienced changes in their lives. Still, the effects were subtle.

However, survivors of NDEs who participated in a study by Akierah Binas and Jamie Gruman, both from the University of Guelph, Canada, reported a desire to engage in work that was more meaningful and fulfilling after their experiences. "I was not interested in doing nonsense," one participant commented. Many of the other participants reported that they had changed careers by shifting their work priorities, with some even going on to start their own companies. Rather than focusing on external measures of success such as salary or titles, they were more interested in living lives that were "authentic" and motivated by a need to make a positive difference, wrote the two researchers in the Conversation. The findings of a previous research are consistent with these observations. "Specifically," NDEs shift individual outlooks on life and can serve as catalysts for transformation, influencing how people relate to others."

The Line Between Life and Death

The boundary between life and death, never distinct to begin with, has only become more blurred. Scientists have found evidence of what they term "a third state," in which the cells of a "dead" organism are not only alive but are also capable of sometimes acquiring new abilities they never had while the organism was alive.

This research, which was published in the journal Physiology, was led by Peter Noble from the University of Washington in Seattle and Alex Pozhitkov from the City of Hope National Medical Center in Duarte, California.

"Life and death are traditionally viewed as opposites," the researchers wrote in the Conversation. "But the emergence of new multicellular life-forms from the cells of a dead organism introduces a ‘third state' that lies beyond the traditional boundaries of life and death."

The cells in this third state demonstrate their new capabilities when given sufficient fuel in the form of nutrients, oxygen, bioelectricity, or biochemical signals. In 2021, for instance, scientists found that skin cells from dead frogs could spontaneously form multicellular organisms—actual living machines called "xenobots." These xenobots used hairlike structures called cilia to move through their surroundings, a behavior they never exhibited while the frogs were alive. These xenobots could also heal themselves and were capable of limited replication.

In another study, it was found that human lung cells derived from dead organisms could self-organize into tiny multicellular organisms known as "anthrobots." Ranging in size from the width of a human hair to the tip of a sharpened pencil, anthrobots can act as multicellular robots capable of self-assembly, self-healing, and repair, and demonstrate a healing effect on damaged nerve cells.

How these xenobots and anthrobots do these astonishing things is a mystery. Some scientists speculate that a hidden circuit of electrical currents animates them or that they require an adequate supply of nutrients and energy before they are reanimated. Other scientists believe that temperature and environment may play an essential role in the ‘postmortem landscape." The unusual behavior of specific cells in this third state does hold out the possibility o finnovative treatments—to dissolve arterial plaque in atherosclerosis, for instance, or clear mucus in people with cystic fibrosis.

It is unlikely we will ever fully understand the causes of near-death experiences, leaving us to rely on survivors' accounts. People readily embrace uplifting stories—less so the disturbing ones—because they seem to affirm belief in life after death. While scientists studying NDEs attribute them to neurological causes, even conclusive findings are unlikely to overturn the widespread conviction that clinical death marks not an end, but a beginning.

Leslie Alan Horvitz is a novelist, journalist, and the science and technology editor at the Observatory. His nonfiction books include Eureka: Scientific Breakthroughs That Changed the World, Understanding Depression (co-authored with Dr. Raymond DePaulo of Johns Hopkins University), and The Essential Book of Weather Lore. His articles have been published in Travel and Leisure, Scholastic, Washington Times, and Insight on the News, among others. He has served on the board of Art Omi and is a member of PEN America. Horvitz is based in New York City. You can find him online at lesliehorvitz.com.

This article was produced for the Observatory by the Independent Media Institute.